Towed vehicle braking system with combined vacuum and pressure supply

ABSTRACT

A towed vehicle braking system is described that in some embodiments includes a brake pedal connector configured to connect to a brake pedal of a brake of a towed vehicle. A cylinder has a piston connected to the brake pedal connector to actuate the brake of the towed vehicle through the brake pedal connector by applying a positive pressure to the brake pedal connector to move the brake pedal. A vacuum supply line is coupled to a power booster of the towed vehicle brake and configured to provide vacuum to the power booster. A pump is coupled to the vacuum supply line and to the cylinder to alternately provide vacuum to the vacuum supply line and to drive the piston to actuate the brake. An inertial sensor detects deceleration of the towed vehicle, and a processor is coupled to the inertial sensor and to the pump to cause the pump to not provide vacuum and to drive the piston in response to the detection of deceleration.

FIELD

The present description relates to towed vehicle braking systems and, inparticular, to a system that is installed into the towed vehicle.

BACKGROUND

It is often convenient to tow one vehicle behind another. A heavytrailer typically provides a separate electric or hydraulic brakingsystem that can be controlled by the tow vehicle through a standardizedinterface. The trailer's brakes can significantly reduce the stoppingdistance of the combination by aiding the tow vehicle in stopping thecombination. Unlike a trailer, a typical towed vehicle, such as anautomobile, a car, or a truck, sometimes called a toad or a dinghy, doesnot have a trailer braking system interface. To reduce stoppingdistances, however, auxiliary braking systems have been developed toactivate the towed vehicle's independent braking system. A particularlypractical, convenient, and effective system rests on the floor of thevehicle cabin in front of the driver's seat and pushes the brake pedalin proportion to when and how the tow vehicle brakes.

The portable braking system that rests on the floor of the vehicle cabindoes not require any modification to the vehicle and so it is easilymoved to another vehicle. At the same time, it must also be disconnectedand moved out of the way each time the vehicle is unhitched to bedriven. It must then be stored out of the way to be re-installed for thenext time it is towed. For this reason, many users choose a towedvehicle braking system that is permanently installed into the vehicle.With these systems, there is a cost to install the braking system and afurther cost if it is ever moved to another vehicle. However, aninstalled system allows the driver to drive the vehicle with theinstalled braking system still in place.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The appended claims set forth the features of the invention withparticularity. The present invention is illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings in which like reference numerals refer to similar elements.

FIG. 1 is a diagram of one vehicle towing another using a towed vehiclebraking system according to embodiments of the invention.

FIG. 2 is a diagram of a portion of an installed towed vehicle brakingsystem and towed vehicle brakes according to embodiments of theinvention.

FIG. 3 is a block diagram of an installed towed vehicle braking systemaccording to embodiments of the invention.

FIG. 4 is a pneumatic valve flow diagram of a brake drive system in aSTANDBY state according to embodiments of the invention.

FIG. 5 is a pneumatic valve flow diagram of a brake drive system in aBOOSTER state according to embodiments of the invention.

FIG. 6 is a pneumatic valve flow diagram of a brake drive system in aBRAKE state with high brake pedal force according to embodiments of theinvention.

FIG. 7 is a pneumatic valve flow diagram of a brake drive system in aBRAKE state with modulation of the brake pedal force according toembodiments of the invention.

FIG. 8 is a state diagram of a brake drive system according toembodiments of the invention.

FIG. 9 is a perspective view of components of a towed vehicle brakingsystem according to embodiments of the invention.

FIG. 10 is a process flow diagram of controlling a brake drive systemaccording to embodiments of the invention.

FIG. 11 is a process flow diagram of controlling an air pump and valvesaccording to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a typical context in which a brake activationsystem such as described herein may be used. A tow vehicle 10 pulls atowed vehicle 12. In the illustration, the tow vehicle is a motor homeand the towed vehicle is a light reconnaissance vehicle. However, thetow vehicle may be any type of car, truck, van, bus, or recreationalvehicle and the towed vehicle may be any lighter vehicle that is towedflat on the ground and has a conventional brake system that is activatedwhen a driver pushes a brake pedal. The tow vehicle has a tow hitch 14and the towed vehicle has a tow bar 16. The tow bar attaches to thehitch for towing. When the towed vehicle is unhitched for separate use,the tow bar is removed or folded out of the way.

The towed vehicle 12 has a breakaway detector 22 near the towed vehiclefront bumper or near the tow bar 16. The breakaway detector is connectedwith an electrical cable or wirelessly to a main controller 24 in thisillustrated example. The breakaway detector alerts the main controllerwhen there is a vehicle breakaway. In this example, the main controlleris in a location under the hood. In some cases, the main controller maybe located at a high position near the battery in a position betterprotected from the road and from engine heat. The main controllerincludes a brake pedal connector 26 with a cable or arm to pull thebrake pedal of the towed vehicle. The main controller actuates the brakepedal in response to a vehicle breakaway and when the tow vehicle isbraking.

The main controller also has a wireless interface to communicate withother parts of the system. In this example, the tow vehicle optionallyhas an access point or hub 28 at the rear of the tow vehicle near awireless interface of the main controller 24. The tow vehicle also has aportable control panel 30 near the driver that is wirelessly coupled tothe main controller directly or through the hub to display statusinformation, such as braking activity, battery activity, or a breakawayalert. In some embodiments, the portable control panel shows otherinformation from the main controller such as operational states, batterystatus, and inertial sensor measurements.

In some embodiments, other devices may be connected to the portablecontrol panel. Tire pressure monitors may be attached to each tire todetermine the pressure at any one or more tires on the tow and towedvehicles. In some embodiments, the tire pressure sensors are attached totire valve stems, for example in the form of a valve cap, and includepressure sensors and wireless transmitters to send the sensed tirepressure to the main controller, the hub, or the portable control panel.These may transmit data for display on the portable control panel. Insome embodiments, cameras may be placed on the towed vehicle or towvehicle, such as backup, side view, and security cameras. These camerasmay wirelessly connect to the portable control panel for control anddisplay. In some embodiments, the portable control panel may be coupledto external information sources such as through the Internet directly,through the hub, or through a smartphone or mobile Internet device. Thisconnection may be used to show weather conditions, travel information,and other information. In some embodiments, the portable control panelhas position sensors or is connected to position sensors and showsmapping and navigation information.

The optional hub in this example provides a wireless link from equipmenton the towed vehicle to the portable control panel. The hub may be arepeater, a wireless router, an access point, or part of a mesh network.The hub may be connected to an external network through an internalsystem or a connection to another wireless hot spot. The hub may be usedto connect users inside the tow vehicle to external networking equipmentoutside the vehicle. As an example, some vehicles use a satellite groundstation mounted on the vehicle for an Internet connection. In someembodiments, the hub is portable and may be removed from a power dockinside the tow vehicle and used in other locations for other purposes.In some embodiments the hub has level sensors and may be placed on thefloor or another surface of the tow vehicle to determine whether thevehicle is level. This data is provided to the portable control panel. Auser outside the tow vehicle may adjust attitude of the tow vehiclewhile referring to level information displayed on the portable controlpanel. The hub may similarly be used to level trailers or other vehiclesand to measure pitch in different situations. In some embodiments, thehub transmits level information when mounted in the dock to the portablecontrol panel. This may be used to provide roll, yaw, and pitchinformation to the driver or passenger while underway. The describedvehicle combination and functions are provided as an example and theremay be more or fewer components with wired or wireless connections.

FIG. 2 is a diagram of a portion of an installed towed vehicle brakingsystem and towed vehicle brakes according to embodiments of theinvention. The interior passenger compartment 62 of the towed vehicle isseparated from the engine compartment 64 by a firewall 72 that becomesor is attached to the floor 70 of the driver's area of the towed vehiclepassenger compartment. In the illustrated example, the towed vehicleinterior floor pan 70 is typically, but not necessarily carpeted. Thefloor pan extends forwards to the firewall 72 between the passengercompartment and the engine compartment. The floor pan also extendsrearwards in the opposite direction to a seat platform (not shown).

The vehicle interior also has a brake pedal 82 suspended from a brakepedal arm 80 used to activate the vehicle's independent braking system.When pressed, the brake pedal arm drives a rod 56 into a brake powerbooster 50. The power booster is coupled to a master cylinder 54 with ahydraulic reservoir so that when the brake pedal is pressed, brake fluidis pushed out of the reservoir through brake lines 58 to drive brakepads or shoes against rotors or drums to slow or stop the towed vehiclewheels. The power booster uses vacuum, typically, but not necessarilysupplied by an engine intake manifold. The power booster increases theeffect of the brake pedal against the master cylinder using the storedvacuum. The power booster reservoir has a vacuum supply line 52 that isconnected to a vacuum source to maintain the vacuum reservoir of thepower booster 50. When the engine is not running the vacuum reservoir ofthe power booster may be replenished by an air pump (not shown) of thebrake drive system as described below. The illustrated configuration isprovided as an example, the invention is not limited to any particularconfiguration or operation of the vehicle's braking system.

In FIG. 2, a clamp 74 is shown attached to the brake pedal arm 80. Theclamp is also attached to a cable 78 including a conduit or a rod thatextends through a conduit connector 76 at the firewall 72. The cable 78extends through the firewall to the engine compartment and attaches to abrake pedal drive system. In this example, the brake pedal drive systemincludes a piston rod 42 in a cylinder 40. The piston rod is attached toa piston 44 that is driven through the cylinder to pull or release thecable 78. When actuated, the piston pulls the cable through the cableconduit through the firewall to the brake pedal arm to pull the brakepedal toward the firewall to engage the brakes of the towed vehicle. Inother words, the piston applies a positive pressure to the brake pedal,through the brake pedal arm. This is the same positive pressure thatwould be applied by a driver with the foot to brake the vehicle.

When de-actuated, the cable tension is released and the brake pedal armreturns to its neutral position so that the towed vehicle brakes arereleased. The vehicle brake system has its own negative pressure thatpushes against the positive pressure of the cable to stop or release thevehicle brakes. This inherent negative pressure of the vehicle brakesmay be used to move the piston back to its initial position when thepositive pressure, generated by the pneumatic system, is released. Inaddition, a spring 48 may be used that is attached to the piston to pushthe piston back to the neutral position at the end of each brakingcycle. Alternatively, the piston may be driven by pneumatic pressure inthe opposite direction to its initial position.

In some embodiments, the piston 44 of the brake drive system is drivenby a pneumatic pressure supply line 46. Pneumatic pressure drives thepiston away from the cable, drawing the cable away from the brake pedalarm toward the firewall actuating the brake. When the pneumatic pressureis released, then the piston is allowed to move through the cylinderback to release the pull on the brake pedal. Various additional valvesand lines may be provided to control the action of the piston. Hydraulicpressure from a suitable pump and reservoir may be used instead ofpneumatic pressure. Alternatively, other brake pedal drive systems maybe used, such as linear motors, solenoids, electromagnetic drives, wormgear drives, stepper motors, driven cable reels, etc. An arm or rod maybe used to drive the brake pedal arm instead of the illustrated cable.For the cable, additional components, such as guides, idlers, pulleys,tension wheels, etc. may be used to control and direct the cable.Similarly, for an arm or rod system, hinges, joints, cams, etc. may beused to direct and control the force on the brake pedal arm. In someembodiments, cables and rods may be combined to convert the action ofthe arm drive system to an appropriate force against the brake pedalarm.

The brake pedal arm clamp 74 may take different forms depending on thenature of the brake pedal arm. The clamp may have a front and rear plateattached on opposite sides of the brake pedal arm by screws or pivotingarms. The clamp may have a circular shape that is wrapped around thebrake pedal arm and then tightened around the arm to remain in place.The clamp may have a pin that extends through the brake pedal arm tohold the clamp in place. The clamp is configured to prevent the cablefrom moving along the length of the brake pedal arm and also to allowthe cable to pivot as the brake pedal moves. The clamp may be attachedto the brake pedal arm, as shown, or to the brake pedal or in any othersuitable location that provides sufficient leverage on the brake systemwithout interfering with an operator driving the towed vehicle.

The system of FIG. 2 is provided as an example only. It may be modifiedin many different ways to suit different applications. More or fewercomponents may be used depending upon cost and accuracy constraints. Inaddition, additional components may be added to provide additionalfunctions other than activating the braking system.

FIG. 3 is a block diagram of an example towed vehicle braking system 300installed into a vehicle. The system may be configured to remain in thetowed vehicle when the vehicle is being towed, driven, and stored. Inthis example, the entire system is operated and controlled by a centralprocessor 344 of the main controller 302, typically in the form of aprogrammed microprocessor or microcontroller with embedded or discreteprogram instructions and operational memory. Any other programmable orhardcoded logic, such as Field Programmable Gate Arrays (FPGAs), TTLlogic, or Application Specific Integrated Circuits (ASICs), mayalternatively be used. Alternatively, there may be multiple independentsubsystems for one or more of the particular functions described herein.The central processor is coupled to at least a brake pedal drive system304 and actuates the brake pedal based on input from an inertial sensormodule 342 and a breakaway module 308. In this example, the brake pedaldrive system includes an air pump or air compressor 310, a brakeactuator 314 in the form of a pneumatic cylinder and piston, a cable 316from the piston to the brake pedal arm 320, and a manifold 312, thatincludes a valve array to control the operation of the piston 314. Thecompressor 310 may be pneumatically coupled to the manifold 312 throughan optional tank 311 or through a pressure reservoir.

The tank may be used to provide a reservoir of pneumatic pressure forimmediate use. The tank allows for a smaller compressor. The compressorprovides pneumatic pressure through hoses or pipes to the manifold 312.The manifold has a valve array operated by solenoids or other actuatorsthat are controlled directly by the central processor 344 or by asubsidiary brake drive system controller (not shown). The manifold 312is coupled to the brake actuator 314 with further hoses or pipes anddistributes the pneumatic pressure to the actuator 314 under the controlof the central processor 344. The air pump or air compressor 310 maycome in many different forms and sized to suit different vehicles anddifferent actuators. The primary function is to pump air from the powerbooster and to the actuator. To simplify reading, it will be referred toas an air pump herein but the term air pump should be construed to meanany suitable compressor or other air handler capable of operating asshown and described.

The actuator 314 drives a cable 316 in response to the distributedpneumatic pressure. The cable extends through the towed vehicle firewall351 and is attached with a clamp 318 to the towed vehicle brake pedalarm or another suitable structure. The cable moves the towed vehiclebrake pedal through a brake pedal arm 320 or any other means to engageand release the towed vehicle brakes. As shown, the brake pedal arm 320and cable clamp 318 are on one side of the firewall 351 in the vehiclepassenger compartment 350. The other components, including the actuator314 are on the other side of the firewall 351 in the vehicle enginecompartment 349. This configuration minimizes the braking system's 300intrusion into the passenger compartment. As mentioned, some of thecomponents may be installed inside the passenger compartment andadditional guides, idlers, or hinges may be installed to improve theoperation of the brake pedal arm. While the braking system 300 isillustrated as a pneumatic system, any other suitable type of brakepedal drive system 314 may be used under control of the centralprocessor 344. The compressor and manifold may be replaced by othersystems or power supplies for an electric system or removed in favor ofa worm gear drive or other actuator.

The manifold 312 has a further optional pneumatic connection to anoptional vehicle brake power booster 322. While many vehicles have avacuum driven brake power booster, some have no brake power booster andothers have electric brakes. In this example, the power booster receivesthe movement of the brake pedal arm through a connection as shown inFIG. 2 and increases the hydraulic pressure applied to the brakes of thetowed vehicle. The power booster uses an internal vacuum reservoir thatis consumed when the towed vehicle brakes are engaged. The vacuumreservoir is connected to the engine air intake manifold by a hose. Theengine creates vacuum at the intake when the towed vehicle is running.The hose maintains the same vacuum at the engine as at the reservoir toreplenish the power booster.

However, when the towed vehicle is being towed, the engine is typicallynot running and is not able to replenish the vacuum reservoir. In someembodiments, a tee fitting in the power booster hose (not shown) betweenthe power booster and the engine allows a vacuum supply line to beconnected from the manifold 312 to the power booster. A vacuum sensor324 is coupled to the vacuum reservoir through the vacuum supply line orin some other suitable location to measure the vacuum pressure in thereservoir. The brake drive system manifold 312 provides vacuum from thecompressor 310 to the power booster in response to the vacuum sensor. Insome embodiments, the vacuum sensor is coupled to the central processor344 and the central processor commands the compressor and manifold toenergize to replenish the power booster as needed. An additionalpressure sensor is coupled between the manifold and the brake drivepiston 314 to measure the pneumatic pressure at the cylinder. Additionalsensors may be used to suit particular implementations.

The central processor is also coupled to a sensor module 342. The sensorarray contains two types of sensors. A first type of sensor 341determines whether the tow vehicle is braking, and if so, then howfirmly. In one example, the sensor receives commands from a trailerwiring system of the tow vehicle (not shown). In another example, thesensor array includes inertial sensors such as accelerometers, pitchsensors, pressure sensors, or other sensors to determine whether the towvehicle is braking. When the sensors determine that the tow vehicle isbraking and this information is sent to the central processor, then thecentral processor can activate the brakes of the towed vehicle throughthe actuator 314 of the brake pedal drive system 304 to assist the towvehicle brakes. The amount of braking or the firmness of the braking canalso be determined using the inertial sensors. In this way, if the towvehicle is braking firmly, then the towed vehicle's brakes will beoperated firmly. On the other hand, if the tow vehicle is braking gentlythen the towed vehicle's brakes may also be operated gently.

A second type of sensor 343 of the sensor module 342 determines theoperational conditions of the braking system 300. For example, sensorsmay measure the pressure in the power booster 322 and the pressure tank311, the condition of the compressor 310, the positions of the valves inthe manifold 312, the position of the piston arm 42, and otherconditions. This information may be used to ensure that the systemoperates as intended. There may also be sensors to determine that thebrake cable 316 is properly attached, that power is being supplied tothe system and other braking system parameters.

The central processor 344 is also coupled to a fixed control panel 338that includes a user interface to receive commands and to provideinformation to the user. The control panel 338 may be in the form ofbuttons, knobs, and lights or a touchscreen or some combination toindicate status and operation conditions. There may be switches or othersuitable command interfaces for power condition, operational mode,sensor status, and any other suitable information and control. A usermay be able to operate and test the braking system at the control panel.

An RF (Radio Frequency) subsystem 340 is coupled to the centralprocessor and provides wireless connectivity and a wireless interface toother components of the system. The RF subsystem includes an RF I/O(Input/Output) port that is coupled through analog RF FE (Front-End)circuitry to an antenna 339. The subsystem 340 may use Wi-Fi, Wi-FiDirect, 5G, Bluetooth, or any other wireless protocol on any suitablefrequency, including unlicensed bands. The transceiver can includemodulators, up-converters, frequency generators, mixers, multiplexers,analog amplifiers and similar components.

The RF subsystem may communicate with the portable control panel 30 withor without an intermediate hub 28 and to other components as describedherein. The portable control panel, and any other connected wirelessterminals such as a smart phone, mobile, device, personal computer, ortablet, may be used instead of or in addition to the fixed control panel338. In one example, the RF subsystem including the RF I/O and RF FEreceives commands and sends status messages to the portable controlpanel 30 in the tow vehicle. The portable control panel provides statusand control that the tow vehicle driver can see and operate from thedriver's seat of the tow vehicle or any other location that is withinrange. Upon arrival at a destination, the portable control panel may beused for other purposes. The two-way connection may be used tofacilitate a variety of different purposes and the portable controlpanel may also be used in the towed vehicle for set up, diagnosis, andoperation. In particular, if the brake sensor or any other sensordetects a fault, then the RF subsystem may send an alert to the portablecontrol panel 30 in the tow vehicle and also activate any other alarmsor alerts, such as on the fixed control panel 338 or using audiblewarnings.

The RF subsystem 340 may also communicate with additional sensors at thehitch, in the towed vehicle, or in the tow vehicle to obtain additionalsensor and brake activation information. The RF subsystem may alsocontain receivers for position information to send position data and analert if the towed vehicle is lost or stolen.

The braking system 300 further optionally includes a breakaway system308. A cable 334 is attached to the tow vehicle (not shown) at one endand attached to a breakaway cable receiver 332 at the other end. Thebreakaway cable receiver detects when the cable is removed, indicatingthat the towed vehicle is no longer connected to the tow vehicle. Any ofa variety of other proximity sensors may be used instead or in addition.The breakaway status of the tow vehicle, for example the presence of thecable, is indicated by the receiver 332 to a status detector 336. Thebreakaway cable receiver 332 may be connected to the breakaway statusdetector 336 by a physical wired or optical bus interface or by a radioconnection either directly between the breakaway cable receiver 332 andthe breakaway status detector 336 or through the RF subsystem 340. Inone example, the breakaway cable receiver is mounted near or on the towbar of the towed vehicle and the breakaway status detector is a part ofthe braking system main controller 302.

The braking system further optionally includes a towed vehicle powercontrol system 306. A power supply circuit 328 is coupled to the centralprocessor 344 and any other appropriate components to provide power at asuitable voltage for the respective component. The power supply circuitconnections are not shown in order not to obscure the other features ofthe braking system 300 but may include connections to the brake drivesystem 304, including the compressor 310, and valve manifold 312, to thesensor module 342, to the fixed control panel 338, to the RF subsystem340, and to other components of the braking system. The power supplycircuit receives power from the tow vehicle battery 326 and convertsthis power as appropriate and regulates the supply circuit to othercomponents. In some installation, the towed vehicle may be towed andbraked for many days before the battery is depleted.

The power control system 306 also optionally maintains the charge statusof the towed vehicle battery 326. A voltage detector 330 monitors thevoltage at the battery. This information is provided to a batterycharger circuit 329 which applies power to the battery 326 as may besuitable to maintain the battery. A DC power source 346, such as the towvehicle electrical system provides power to the charger circuit that isregulated and applied to the battery. In some embodiments, the towvehicle trailer harness has a socket connector to receive a plug 348from the tow vehicle. This plug is wired into the battery chargercircuit 329 as shown. There are a variety of suitable socket and plugsystems with two to seven or more connectors and in different flat orround shapes. For battery charging purposes the plug 348 requires onlytwo connectors, however any other connector that provides power may beused.

In some embodiments, the tow vehicle does not have a trailer harness butonly a suitable power supply connector. In some embodiments, the plug isconnected to the main controller with a cable, such as a 2 or 4 wireelectrical cable, that extends from the main controller in the enginecompartment far enough to reach the socket of the tow vehicle. Thisallows the power to be connected without accessing the enginecompartment of the towed vehicle. In some embodiments, the maincontroller is connected to a cable that extends to a socket at theexterior front of the towed vehicle at which the cable is connected. Inorder to make the electrical connection, an operator uses a cable with aplug at each end. One end is plugged into the socket on the tow vehicleand the other end is connected to the socket on the towed vehicle.

The power supply circuit may power the braking system using power fromthe tow vehicle DC power source 346 and using battery power 326 of thetowed vehicle. The towed vehicle battery provides a reservoir of highcurrent power for sudden high power demands and also allows the brakingsystem to be operational when it is not connected to the tow vehicle orwhen the tow vehicle is not generating power to the towed vehicle. Bymaintaining the battery 326 when the tow vehicle DC power source 346 isavailable, the reliability of the braking system 300 is enhanced. Inaddition, the towed vehicle is maintained in a state that is ready forindependent operation after it is unhitched from the tow vehicle. Insome embodiments, the power supply circuit draws power only from thebattery. The battery charger circuit and tow vehicle connection may beexcluded or provided as an independent and separate unit.

There are a variety of techniques and methods for maintaining theelectrical condition of a battery and these may differ for differenttypes of batteries. The specific timing and power characteristicsapplied to the battery may be adapted to suit any particular type ofbattery. The technique may be driven by the central processor orindependently by the power control system 306 or battery charger circuit329. In some embodiments, a battery charger controller operates in threestages. In the first stage, a high current, e.g. 3 A to 10 A is appliedto the battery when the battery is below a first threshold such as 70%to 90% of its fully charged state. In the second stage, a low current,e.g. 0.3 A to 1 A is applied to the battery when the battery is notfully charged, but above the first threshold. In the third stage thebattery is fully charged but is allowed to fall below a second thresholdsuch as 95% to 98% charged. The low current is applied periodically tomaintain the battery between the second threshold and a fully chargedstate. When the towed vehicle braking system is actuated, a high currentis applied to the air pump and other components and the battery isrecharged over a longer period of time in between braking actuations sothat it is ready for the next braking and also ready to start the towedvehicle engine when the towed vehicle is unhitched.

The voltage sensor 330 allows the braking system 300 to determine thevoltage of the battery at any time. For a common lead-acid 12-voltvehicle system, the battery voltage will be no more than 12.9 volts,when the battery is fully charged. A working battery will typically haveabout 12 volts and may operate at less than 12 volts when partiallydischarged, but should not have more than 12.9 volts. Other types ofbatteries similarly have a fully charged voltage. For example, somevehicles operate partially or fully with 48V electrical systems. Whenthe towed vehicle engine is started, then the engine drives analternator 327 that applies power to the battery. The power applied tothe battery increases the voltage, as measured at the battery beyond themaximum fully charged voltage. The voltage detector 330 is thereby ableto determine when the towed vehicle engine is running based on thevoltage at the towed vehicle battery. This information may be providedto the central processor 344 directly or through the power controlsystem 306. As an example, there may be a predetermined threshold of 12volts or 12.9 volts or another value. When the voltage is above thethreshold, then the braking system may declare that the alternator isoperating and the towed vehicle engine is on. When the voltage is belowthe threshold, then the towed vehicle engine is off.

As shown, the braking system 300 is positioned in the engine compartmentin front of the towed vehicle firewall 351 and outside of the passengercompartment 350. By placing almost all of the braking system under thehood in the engine compartment it is easily accessed when necessary butis out of the way of the driver and passengers. This position providesconvenient access to the brake power booster 322, breakaway cable 334and battery 326. The engine compartment is also closest to the towvehicle which enhances communication with the hub 28 and tablet 30. Insome towed vehicles, this front compartment may not include an engine,the brakes, a battery or some combination of the three and the firewall351 is not for fire. It is only a wall perhaps by another name.Nonetheless, almost every vehicle has a compartment of some kind that isin front of the driver, that is separated from the driver by a wall, andthat includes access to the vehicle brakes. In this description, thisfront compartment will be referred to as the engine compartment. This isfor convenience and does not exclude rear engine, cab over, electricwheel hub motors and other types of vehicles.

As shown in this example, the power control system 306, centralprocessor 344, sensor module 342, breakaway status detector 336, RFsubsystem 340 and fixed control panel 338 are all part of a maincontroller 302. These components may be built on a single circuit boardor on multiple circuit boards. In either case all of these componentsmay be mounted within a single housing that surrounds and encloses thecomponents. The housing is useful to protect the components from dirtand moisture that may be common in an engine compartment. The maincontroller may be configured as a single compact unit in a singlehousing with external connectors. All or some of the components may beincorporated into a single integrated circuit. By providing the controlboard as a single unit in one housing, the installation of the brakingsystem is simplified. As shown the main controller has only a fewexternal connections. These external connections are to the breakawaycable receiver 332, the towed vehicle battery 326, the tow vehicle DCpower source 346, such as through a trailer brake system, and the brakedrive system 304 of compressor 310, manifold 312 and sensors 324. Thissimplified approach with four external connections allows the brakingsystem to be quickly and easily installed. As mentioned, the externalpower connection is optional.

The RF subsystem allows additional equipment and functions to beinstalled without making any physical connections to the main controller302. Additional functions may include vehicle tire pressure, vehiclebrake light status, vehicle position, attitude, and other features.

In the illustrated embodiments and as shown for example by the breakawaydetector 22 in FIG. 1, the braking system configuration allows thesystem to be operated without opening the hood of the vehicle, that iswithout opening the engine compartment. The user can attach thebreakaway cable 334 to the cable receiver 332 at the front of the towedvehicle, for example on or under the front bumper. The user mayoptionally attach the power supply plug 348 to the tow vehicleelectrical harness typically near the tow vehicle hitch. The RFsubsystem and the portable control panel the allow the user full controlover the connected and active towed vehicle braking system withoutopening the hood of the vehicle or accessing the engine compartment.Similarly, the towed vehicle braking system may be disconnected from thetow vehicle and shut off by unhitching, removing the breakaway cable,and disconnecting the power plug. The portable control panel providesaccess to all of the main controller features and functions.

To operate the actuator 314, in the form of a pneumatic cylinder, thereis at least one valve in the manifold 312 that releases air from thecompressor 310 into the cylinder to drive the piston away the brake.There may be another valve to release air from the cylinder to allow thepiston to move freely or to drive the piston toward the brake. One ormore pressure sensors in or around the cylinder may be used to determinewhether the cylinder is energized and in which directions.

As mentioned above, the towed vehicle braking system uses a battery 326coupled to a power supply system 306 to power the main controller 302and all of the other components of the braking system. The controlleroperates the brake drive system 304, such as a compressor, manifold, andactuator. The brake drive system is coupled to the brake pedal connector318 that is configured to connect to a brake pedal of the brake of thetowed vehicle. The brake drive system is connected to the brake pedalconnector to actuate the brake of the towed vehicle through the brakepedal connector by applying a positive pressure to the brake pedalconnector to move the brake pedal. The main controller 302 includes aninertial sensor 341 to detect deceleration of the towed vehicle. Thecontroller then causes the operation of the brake drive system inresponse to the inertial sensor.

In the illustrated examples, the battery 326 is the main towed vehiclebattery that is used to power all towed vehicle electrical systems andthat is maintained by the towed vehicle engine. The towed vehicle engineprovides mechanical energy to an alternator 327 which converts themechanical energy into electrical energy to charge the battery. Thealternator may include or be connected to a voltage regulator (notshown) to control the charge applied to the battery by the alternator.This battery is connected to the power supply system 328 and providessufficient power to operate the towed vehicle braking system when thetowed vehicle engine is off.

The power control system 306 may be connected to a DC power source 346of a tow vehicle. This connection may be through a conventionalelectrical trailer connector or through another electrical connector tothe electrical system of the tow vehicle. When the tow vehicle isconnected, then it provides DC power to the power supply system 328.This power may be used to power the main controller 302 and it may beused to power a battery charger circuit 329. The battery charger circuitis particularly useful to charge the battery when the towed vehicleengine is off and the towed vehicle is being towed by the tow vehicle.Because the brake drive system 808 is used only rarely, the battery maybe charged slowly but provide a reserve of much greater power throughthe power supply system when the brake drive system is operated.

The voltage detector 330 monitors the voltage of the battery. It iscoupled to the battery charger circuit 329 so that the battery chargercircuit can regulate the power supplied to the battery based on thecharge state or voltage of the battery. The voltage detector is alsoconnected directly or through the battery charger circuit to an ON/OFFcircuit of the main controller. The ON/OFF circuit turns on or off thebrake drive system based on the measured voltage. The voltage detectorprovides a signal, such as a voltage, a digital output value, or analert that represents the voltage of the battery. In some embodiments, avoltage output of the voltage detector is sampled at the charger circuitand converted into a digital representation of the voltage. In someembodiments, the voltage detector applies the detected voltage to one ormore internal thresholds and provides a digital value or an alert toindicate one of multiple different ranges that the battery voltage iswithin.

The ON/OFF circuit turns the brake drive system off when the detectedvoltage is indicated as being above a threshold. A battery voltage abovea threshold, such as 12 volts, indicates that the battery is beingcharged by the alternator. This indicates that the towed vehicle engineis on and someone is driving the towed vehicle apart from the towvehicle. By turning off the brake drive system, the driver's control ofthe vehicle is unimpeded. If the battery voltage is below the samethreshold or another lower threshold, then the ON/OFF circuit turns onthe brake drive system. The lower voltage indicates that the towedvehicle engine is off and the towed vehicle is not being driven. Thethreshold may be configured to suit different vehicles that operate atdifferent voltages or that have batteries that operate at differentvoltages. Currently some vehicles operate at 48 volts and older orsmaller vehicles may operate at 6 volts, but any other threshold may beused depending on the towed vehicle.

By providing the ON/OFF circuit, an operator need not manually turn thetowed vehicle braking system on and off. In some embodiments, the towedvehicle braking system does not have an on/off switch but automaticallydetermines when to turn the brake drive system on and off using thebattery voltage. In some embodiments, the user is able to turn the towedvehicle system on and off using an integrated control panel or aportable control panel or other mobile device. The ON/OFF circuit isable to intervene as an additional safety feature in the event that theuser fails to turn off the towed vehicle braking system.

Additional inputs may be used to complement or replace the batteryvoltage detector 330 as an input to the ON/OFF circuit 820. The towvehicle input DC power connection 348 may be used as an input. Thispower is provided only when the towed vehicle is attached to the towvehicle. Accordingly, if there is no input power, then it may beinferred that the towed vehicle is not being towed and the brake drivesystem may be turned off. If there is input power then the towed vehicleis attached to the tow vehicle and the brake drive system is turned on.A breakaway detection system may be used as an input. If the breakawaycable is attached to the breakaway detector, then the towed vehicle isbeing towed and the brake drive system is turned on. Additional inputsand connectors may be used to suit different implementations. These twoinputs may be combined with the battery voltage and the inertial sensorsto determine ON/OFF status.

FIG. 4 is a diagram of a pneumatic system in an active state ready tomove to states for maintaining a vacuum in the power booster and fordriving the cylinder to operate the brakes with a single compressor.This is done in part by use of a manifold 402 as described above. Themanifold is controlled by the central processor based on the state ofthe braking system 300. The central processor uses the sensors todetermine the state of the towed vehicle and then configures themanifold and other components for the particular state. In the exampleof FIG. 4, the braking system 300 is at rest and the manifold isconfigured for initial active state. This state is entered on initialactivation, upon system deactivation, such as when the towed vehicle isbeing driven and is no longer being towed, and during much of the timethat the towed vehicle is being towed.

The manifold 402 of FIG. 4, is coupled to a single air pump or aircompressor 404 as it is labeled in the drawing figure. The air pump hasa high pneumatic pressure output line 405 through the manifold to apneumatic cylinder input line 407 to a cylinder 406. The cylinder has apiston to drive a brake pedal as discussed above. In this example, thepiston is driven by the single pneumatic pressure input line 407 toalternately drive or release the piston. In the illustrated example, thepiston is shown as being biased against the pneumatic pressure by aspring so that when the pneumatic pressure is released the spring pushesthe piston back to the neutral or brakes off position. Other pistondrive configurations may be used to suit other types of cylinders andmanifolds. In some embodiments, pneumatic pressure is applied on bothsides of the piston to drive the piston in either direction. The airpump 404 has a vacuum inlet line 403 that connects through the manifold402 to a vacuum supply line 409 of a brake power booster 408.

In this configuration, the air pump, when activated draws air from thevacuum inlet 403 and drives the air out the pressure outlet 405. Themanifold operates valves 421, 422, 423 in response to pressure sensors426, 427 and commands from the braking system central processor todetermine how the air pump is connected. In this way the manifoldcontrols the functions that the braking system performs. In theillustrated embodiment, the air pump either provides vacuum to the powerbooster or pressure to the brake actuation cylinder but not both. As aresult, a less powerful compressor is necessary than would be necessaryto perform both tasks simultaneously. Because the brake power booster ismaintained with vacuum, the power booster is operational even withoutthe vehicle engine operating. The brake actuator benefits from the powerbooster when it actuates the brakes. This also allows for a lesspowerful compressor than if the brake actuator were operating the brakeswithout power assist. The illustrated configuration may be modified tosuit other compressors and other brake systems.

In the active state, the vacuum in the power booster 408 is held and theactuation cylinder 406 is free to move. The air pump 404 is open toatmosphere. In other words, if the air pump were activated it would drawair from atmosphere and push it out to atmosphere.

This resting state configuration is employed under two very differentconditions. In the first condition the system is off. The towed vehicleis not being towed. It may be parked or being driven and so the brakingsystem is deactivated. In this condition, no operations are performed.The second condition is most of the time during which the towed vehicleis being towed. Most of this time, the tow vehicle and towed vehicle aremoving along the road connected together without any braking. In thiscondition, the braking system is activated and standing by ready toperform braking functions. The braking system is monitoring conditionsto determine when to charge the power booster and when to brake. Tofacilitate this active state there are two pressure sensors in theillustrated manifold 402. A vacuum pressure sensor 426 monitors vacuumat the power booster. As long as the booster vacuum is high enough, noaction is taken. A cylinder pressure sensor 427 monitors the pressure atthe cylinder to ensure that there is no significant pressure and thepiston is able to move freely in the cylinder.

In FIG. 4, the manifold has three valves to control the effect of theair pump. These are shown as 3-way NC (Normally Closed) valves but othertypes of valves or combinations of valves may be used alternatively. Thefirst 421 of the three valves, the booster valve, has a first portcoupled directly to the power booster 408 vacuum inlet 409, a secondport is coupled to the air pump vacuum inlet 403 and a third port iscoupled to the atmospheric ambient air. In the active state, the airpump vacuum inlet is coupled to the ambient and the power booster lineis blocked. This setting allows the air pump to take in ambient air andprevents any leakage of the vacuum from the power booster. The 3-wayvalve 421 has two positions, the first is vented to atmosphere as shownand the second is energized as shown in FIG. 5.

A second 3-way valve 422, a cylinder valve, is connected to the cylinder406 in a similar way to the first valve. The first port is coupleddirectly to the cylinder pressure input line 407. The second port iscoupled directly to the air pump pressure outlet 405 and the third portis coupled to the atmospheric ambient air. As with the vacuum line, inthe active state the air pump pressure outlet port is coupled to theambient port and the cylinder port is blocked. This first of the twopositions is a vented position. The second position of the cylindervalve 422 is energized as shown in FIG. 6 to drive the brake actuator406. This vented setting allows the air pump to provide air pressure onthe line without affecting any other part of the system by venting anypressure to ambient. The air in the cylinder is maintained in thecylinder by the cylinder valve 422. The air pump is not operated in theactive state, but even if it is, the inlet and outlet are open toatmosphere, so air pump operation will not affect the pressure on thebooster or the cylinder.

The manifold has a third cylinder relief valve 423 between the cylindervalve 422 and the cylinder. The cylinder relief valve has a first portthat is blocked, a second port coupled to the cylinder pressure line 407and a third line coupled to the atmospheric ambient air. In the activestate, as shown, the cylinder relief valve 423 connects the cylinderpressure at the second port to the ambient at the third port. This is avented position of the valve. This valve allows any pressure in thecylinder to be released while the cylinder valve prevents the air pumpfrom applying any pressure to the cylinder. The brake pedal in theactive state is free to move through its entire travel and its positionis not affected by the air pump. The second position of the cylinderrelief valve is blocked as shown in FIG. 6.

FIG. 5 is a diagram of the pneumatic system in the booster maintenanceor booster state. The system will enter the booster state in response tothe booster pressure being low as measured by the booster pressuresensor 426 and the brakes not being actuated as determined by thecentral processor based on the sensors. The first valve 421 is operatedto connect the first port coupled to the booster vacuum line 409 to theair pump or air compressor vacuum inlet 403. This is the energizedposition. The second and third valves are not moved. The air pump isoperated to pump air out of the power booster through the vacuum line409 to the booster and out to ambient through the second valve 422.After the vacuum pressure is sufficient, full, or high enough asmeasured by the vacuum pressure sensor 426, then the air pump can bedeactivated and the first valve moved to the active state. The other twovalves 422, 423 are not changed from the active state. This allows theair pump to exhaust air into the atmosphere through the cylinder valve422 while operating as a vacuum pump for the power booster.

FIG. 6 is a diagram of the pneumatic system in a first part of the brakestate. The system enters the brake state when the central processordetermines that the towed vehicle brakes should be energized by thebrake actuator 406. This state will be entered without regard to thecondition of the power booster vacuum. To enter the brake state, thebooster valve 421 is placed in the vented condition as in the activestate. The air pump when activated draws air through the booster valve421 to supply to the cylinder. The cylinder valve 422 is energized toallow the air pump to supply pressure to the cylinder input line. Thisdrives the piston in the cylinder of the brake actuator. The cylinderrelief valve 423 is blocked. The blocked cylinder relief valve 423forces the air to the cylinder with no exit to atmosphere. This appliesthe maximum amount of compressed air to the cylinder to effect a swiftand sure brake pedal action.

During the brake state, the cylinder pressure sensor 427 may be read todetermine the pressure in the cylinder and control the pressuregenerated by the air pump. In this way, the force applied to the brakepedal by the actuator may be adjusted. In some embodiments, the amountof deceleration is monitored by the central processor 344 using theconnected inertial sensors 342. The force applied to the brakes by thebrake actuator 314 is adjusted to correspond to the amount ofdeceleration. In many braking circumstances, a tow vehicle driver willbrake gently and then release the brakes or will change the pressureagainst the brakes during a single braking period. The central processormoderates the amount of braking of the towed vehicle by adjusting theoperation of the air pump in response to the cylinder pressure sensorand the inertial sensors. This allows the central processor and the airmanifold to align the towed vehicle braking with the tow vehiclebraking.

FIG. 7 is a diagram of the pneumatic system in a second part of thebrake state in which the brake pedal positive pressure is modulated. Thesystem has already entered the brake state in response to the maincontroller command as shown in FIG. 6. The booster valve 421 is placedin the vented condition, the air pump is activated, and the cylindervalve 422 is energized to allow the air pump to supply pressure to thecylinder input line. In this part of the brake state, the cylinderrelief valve 423 is vented to moderate the force applied to the brakesby the brake actuator 314. The relief valve may be quickly opened andclosed to adjust the positive pressure to correspond to the amount ofdeceleration. The central processor opens the relief valve 423 toatmosphere without opening the cylinder valve 422 in order to bleedpressure from the cylinder to further reduce the braking force. Eitherone or both of the two controls, air pump operation and valve position,allow a fine degree of control over the brake pedal pressure. It alsoallows the central processor to apply and release the brakes veryquickly.

In FIGS. 6 and 7 the same cylinder relief valve is presented in twodifferent possible states. The first state, represented in FIG. 6, isblocked to allow the full force of the air pump to be applied againstthe cylinder. The second state of the same valve, represented in FIG. 7,is vented to allow pressure in the cylinder to be released. In thispneumatic configuration, the piston is biased to the no braking positionby a spring. Accordingly, when the relief valve goes to the ventposition, the piston, under the force of the spring pushes the air outthrough the relief valve. The amount of released air will depend on theamount of the time that the valve is open. With enough time, thepressure against the brake pedal will be completely relieved.

The controller can use the amount of open time and the amount of shuttime as a type of pulse width modulation to reduce the positivepressure. The relieve valve may be opened with e.g. a 20% duty cycle toreduce the positive pressure moderately and opened with e.g. a 60% dutycycle to reduce the positive pressure significantly. The particularduration of each valve opening for each time period may be adjustedbased on the cylinder pressure sensor and the accelerometer. The desiredduty cycle may depend on the response of the towed vehicle's brakes, thevacuum pressure in the booster and the configuration of the vehiclebraking system such as the power of the air pump, the size of the airsupply tubes, and the flow rate through the relief valve.

In other embodiments additional valves allow the compressed air to beapplied to the cylinder on either side of the piston to drive the pistonin one direction or the other. This allows the piston to quickly move ineither direction with no need for a spring. In another embodiment, thebrake is operated with a motor connected to a cable spool, worm gear,linear actuator or another system. In such embodiments, no manifold orcylinder pressure sensor is used but other sensors may be used toprovide feedback about brake operation. With any actuator, the systemmay still have an active state, a boost state, and a brake state. Thestates do not depend on the nature of the actuator.

FIG. 8 is a state diagram showing transitions between states describedabove, i.e. active, booster, and brake. There are also additionalstandby, sleep and breakaway states. As the towed vehicle is driven intoposition behind the tow vehicle, the braking system begins in a STANDBYstate 802. When the tow vehicle engine is shut down, the braking systemthen moves to the ACTIVE state 804. In some embodiments, the systemmoves to the ACTIVE state 804 in response to detecting a low batteryvoltage at the battery voltage sensor 330. The braking system returns tothe STANDBY state upon receiving an operator command or another sensorinput, such as detecting a high battery voltage. The high batteryvoltage indicates that the towed vehicle engine is running and thealternator is charging the battery. The low battery voltage indicatesthat the towed vehicle is shut down or off. The system may also be movedto the ACTIVE state by an operator operating a control on the fixed orportable control panel or by the central processor sensing some othercondition.

The difference between the low and high battery voltage may bedetermined by comparing the voltage to a suitable predetermined batteryvoltage threshold. As an example, the threshold may be 12 volts for atypical automotive application. If the battery voltage is above the 12Vthreshold, then the braking system goes to the STANDBY state. If thebattery voltage is below the 12V threshold, then the braking system goesto the ACTIVE state. For other vehicles a higher or lower threshold maybe used. The threshold may be pre-configured or programmed into aconfiguration register of the voltage detector, the central processor,or another component by an installer or user using a control panel.While a simple threshold system is described herein, additional criteriaand more complex decision systems may be used to suit particularimplementations. The particular thresholds are provided as examples andmay be modified to suit particular batteries and operating parameters.

The braking system moves from the ACTIVE state 804 and enters the BRAKEstate 808 upon detecting braking by the tow vehicle. The braking systemexits from the BRAKE state 808 and enters the ACTIVE state 804 when itdetects that the tow vehicle is no longer braking. As mentioned above,the BRAKE state may have two parts for high pressure and for modulatedpressure as the system adjusts the braking pressure to match thedeceleration of the towing vehicle. The modulated pressure providesbetter braking and reduced wear than systems that only allow for onelevel of braking to meet all conditions.

The braking system enters the BOOSTER state 806 upon detecting a lowvacuum pressure in the brake booster. This occurs only when tow vehiclebraking also is not detected. If tow vehicle braking is detected, thenthe low vacuum pressure is superseded by the need for braking and thesystem will nevertheless move to the BRAKE state regardless of thebooster vacuum pressure as measured by the booster pressure sensor. Thebraking system moves from the BOOSTER state back to the ACTIVE statewhen the vacuum reservoir of the power booster is full. The brakingsystem will also enter the ACTIVE state when braking is detected. Thebraking system is then able to enter the BRAKE state 808 from the ACTIVEstate.

The central processor 344 is coupled to the vacuum sensor 324 todetermine whether the vacuum reservoir in the power booster is low orfull. In some embodiments, the vacuum sensor sends a voltage that isrelated to the sensed vacuum to the central processor. The centralprocessor measures the voltage to determine whether the vacuum is belowa predetermined vacuum threshold. If so then it commands the transitionto the BOOSTER state. A software threshold allows the threshold to bemodified in software to suit different vehicles. In some embodiments,the vacuum sensor compares the sensed vacuum to a reference thresholdand then sends a signal to the central processor when the vacuum isbelow the reference value. This simplifies the operation of the centralprocessor.

The ACTIVE state allows all valves and sensors to be normalized inpreparation for the next state change. The brake drive system is activeand ready to respond to commands. In some embodiments, the valvesrespond within fractions of a second and the air pump is powered on oroff within fractions of a second. Accordingly, returning to the ACTIVEstate helps ensure proper operation of the braking system. In someembodiments, braking must be applied very quickly and so the brakingsystem has an optional transition from the BOOSTER state direct to theBRAKE state. In the pneumatic system of FIGS. 5 and 6, such a transitionrequires that all three valves be changed but that the air pump stayenergized. If the valves respond to state changes more quickly than theair pump, then the optional path to exit the BOOSTER state and enter theBRAKE state will allow for a quicker response in a move to the BRAKEstate.

The towed vehicle braking system enters a BREAKAWAY state 810 when thebreakaway cable 336 is removed from the cable receiver 332. Thebreakaway system 308 operates to determine when the towed vehiclebecomes unhitched during towing. In the BREAKAWAY state 810, the brakesare applied by the active brake drive system to stop the towed vehicle.This reduces the danger of the towed vehicle rolling free from the towvehicle in transit. The BREAKAWAY state is only available as atransition from the ACTIVE state. As a result, when the towed vehicleengine is started in order to drive the towed vehicle, the brakingsystem enters the STANDBY state and the braking system releases thetowed vehicle's brakes allowing the vehicle to be driven. In someembodiments a user can force a transition from the BREAKAWAY state tothe STANDBY or ACTIVE states using the fixed or portable control panel.

In the example ACTIVE 804, BOOSTER 806, BRAKE 808, and BREAKAWAY 810states described herein the main controller 302, brake drive system 304,power control system 306 and breakaway system 308 are all fully activeincluding the RF subsystem 340 of the main controller. The brake drivesystem 304 and the RF subsystem 340 in particular consume some powerwhen active. The other systems may be fabricated from lower power andprimarily solid state and integrated circuit components that consumevery little power. In some embodiments, the main controller may operatefor months without the RF subsystem with no significant impact on thetowed vehicle battery.

In the STANDBY state the main controller 302 stays active, but the brakedrive system 304 and breakaway system 304 may be turned off as thesewill not be used. This allows the driver to interact with the systemthrough the portable control panel or any other wireless or wiredinterface but it reduces power consumption and any chance of undesiredautomated braking. Turning off the brake drive system prevents the brakedrive system from applying the positive pressure to the brake pedalconnector to activate the towed vehicle brakes.

In some embodiments, the towed vehicle braking system has a SLEEP state812 to reduce power consumed by the system when the towed vehicle isneither being towed or operated. The SLEEP state 812 allows the brakedrive system 304 and the breakaway system 308 to be turned off. Thepower control system 306 is still active to provide power to the maincontroller active components. Power to the other components may bedisconnected to reduce consumption. In the SLEEP state the inertialsensor module 342 is active and coupled to the central processor 344 todetect motion of the towed vehicle. In some embodiments, if there is nodetected motion for a predetermined time duration, e.g. two to sixhours, then the system enters the SLEEP state. In the SLEEP state, inaddition to powering off the brake drive system and the breakawaysystem, the RF subsystem 340 is placed in a low power mode.

In normal operation, such as in any of the other states, the RFsubsystem is operational and active to communicate with any of theconnected external components. This allows the portable control panel tobe fully operational and also allows the braking system to benefit fromany other connected components. When the towed vehicle is parked orstored, then there is no need for immediate communications with anyexternal components. In some embodiments, the RF subsystem is turned offand consumes no power. In some embodiments, the RF subsystem is placedin a receive only mode. Receiving requires much less power thantransmitting. In some embodiment, the RF subsystem is placed in aperiodic wake mode. In this mode, the RF subsystem wakes periodically totransmit a general announcement or advertisement that makes itaccessible to external components. If it receives no reply, then itpowers off until the end of the next time period. The period may be 2minutes, 5 minutes, 10 minutes, or another time period. The particularconfiguration of the RF subsystem in the SLEEP state may be modified tosuit the particular wireless protocols and standards being used. In someembodiments, the RF subsystem shuts down higher power radios, such asWi-Fi and unlicensed band operation and uses only lower power radiossuch as Bluetooth or NFC (Near Field Communications). In someembodiments, the SLEEP state turns off the RF subsystem entirely.

To exit the SLEEP state 812, the central processor receives input fromthe inertial sensor module indicating that the towed vehicle is beingmoved. In some embodiments, the movement is detected by accelerometersin roll, pitch or yaw axes. The sensor module may be responding to thevehicle being towed or a driver entering the vehicle or any othermovement in any axis. The system then moves to the ACTIVE state 804.

In one use case, the towed vehicle is towed to a location with thebraking system in the ACTIVE state. The towed and tow vehicle are thenparked. After the predetermined timer expires, the braking system entersthe SLEEP state. When the tow vehicle then starts up and moves back tothe highway, the movement along the road is detected by the sensormodule which transitions the braking system back to the ACTIVE state.These operations are performed by the braking system automaticallywithout any interaction from any person.

In another use case, the towed vehicle is unhitched from the tow vehicleand driven to a parking spot. While being driven, the tow vehicle is inthe STANDBY state. When the tow vehicle is parked and the engine isturned off, the braking system transitions to the ACTIVE state. Afterthe timer elapses, the braking system transitions to the SLEEP state.When a driver returns and enters the vehicle, the corresponding motionof the vehicle is detected and the braking system transitions to theACTIVE state. In an alternative embodiment, the braking system is ableto transition directly to the STANDBY state when a high battery voltageis detected for example when the driver starts the engine to remove itfrom the parking spot. By transitioning directly to the STANDBY state,the braking system is able to take advantage of the power supplied bythe vehicle to provide complete operation to the user.

In another use case, the braking system uses other or additional inputsto determine whether the towed vehicle is attached to the tow vehicleand is ready to or is being towed. The tow vehicle is ready to be towedwhen the breakaway cable is coupled to the cable receiver. Accordingly,in an embodiment, the main controller determines the breakaway cablestatus and if the cable is in the receiver, then transitions from theSLEEP state to the ACTIVE state. In another embodiment, the power supplycircuit 306 detects that power 346 is being supplied from the towvehicle through the trailer harness plug 348. This status is received atthe processor 344 and the processor transitions the braking system fromthe SLEEP state to the ACTIVE state. Alternatively, both the breakawaycable and the external power must be connected to transition the brakingsystem to the ACTIVE state. In another embodiment these two inputs arecombined with the detection of acceleration in the inertial sensors forthe controller to cause the transition to the ACTIVE state. Theseoperations may be configured based on the configuration of the brakingsystem and any external components. The configurations may be entered byan operator through the fixed or portable control panel.

The state transitions of FIG. 8 may be driven by the central processor344. As described in the context of FIG. 3, the central processor iscoupled to the inertial sensor module 342, to the battery voltagedetector 330 and to the brake drive system 304. The central processorincludes internal clocks for operating timers that may be used to wakeor turn off any or all of the parts of the main controller 302 and theother connected systems. The central processor may include a statetransition engine as a software routine or module or there may be adedicated portion of the central processor that operates the statetransition engine in hardware or firmware. Alternatively, there may bean independent module within or outside of the central controller tooperate as a state transition engine. As explained above, the statetransition engine turns various components on or off depending on theactive state. This engine may be referred to an ON/OFF circuit that isimplemented as hardware or software inside or outside of the centralprocessor. The ON/OFF circuit operates to turn on and off the brakedrive system to support the STANDBY and SLEEP states and also to turn onand off the breakaway system and RF subsystem to support the STANDBY andSLEEP states. The ON/OFF circuit may be configured to respond to thepredetermined voltage threshold as described above.

FIG. 9 is an illustration of components of the vehicle braking systemincluding the main controller 302, the brake drive system 304 and theportable control panel 30. The main controller is contained within ahousing with four external connectors 812, 814, 816, 818. An externalfixed control panel has status indicators 815, 817, 819 associated withthe connectors. Buttons or switches may optionally be included. Theantenna 339 of the RF subsystem 340 is mounted within the housing and isnot shown. The connectors include a breakaway detector connector 812, abattery power connector 814, a brake drive system connector 816 and atrailer harness power input connector 818. These connectors each arecoupled to the respective internal components of the main controller asshown in FIG. 3, i.e. the breakaway status detector 336, the powersupply circuit 328, the processor 344, and the battery charger circuit329, respectively. The main controller housing includes tabs to allow itto be mounted conveniently in the engine compartment of the towedvehicle. The housing has a central seam around the outer periphery ofthe sides of the housing and encloses the components on all sidessurrounding the internal parts for protection. In some embodiments, thehousing has a base to which many of the components are mounted and acover attached over the base to enclose the components.

The brake drive system 304 has an external connector 826 to the maincontroller. The illustrated brake drive system includes the air pump 310and the manifold 312 as well as the pressure sensors 324, 325. Theactuator 314, such as a cylinder is not within the brake drive systemhousing. Accordingly, the brake drive system has an external pressurefitting 824 that connects to a pressure fitting on the cylinder to drivethe cylinder to actuate the towed vehicle brakes. The brake drive systemsimilarly has a vacuum hose fitting 822 to connect to a vacuum supplyhose to the power booster. This portion of the brake drive systemhousing also has tabs to allow it to be mounted in the vehicle enginecompartment. In other embodiments, the cylinder is within the housing oranother type of actuator such as a hydraulic, electric, or motorizedactuator may be mounted within or outside the brake drive system housingwith appropriate connectors. The brake drive system is also enclosedwithin a housing for protection from the environment of the enginecompartment. A seam around the perimeter sides of the housing allows thehousing to be opened for service. Alternatively, the seam may be inanother place on the housing for example between a base and a cover or apan and a lid to suit particular implementations.

The portable control panel 30 has a wireless connection to the maincontroller through which the entire towed vehicle braking system may becontrolled. An antenna is concealed within the housing and not shown. Asmentioned above, the portable control panel may be moved to differentlocations to operate the towed vehicle braking system as is convenientfor the user. In this view, the tablet shows a braking status display802 to indicate that the towed vehicle brakes are being applied by thebraking system. This allows the user to observe what if any actions arebeing performed by the main controller 302. The tablet may also allowthe user to manually apply the brakes, release the brakes and turn thetowed vehicle braking system on or off, among other functions.

FIG. 10 is a process flow diagram for controlling the power of the brakedrive system. This process may be performed by an ON/OFF circuit or bythe central processor 344, or by a part of the power control system 306,or by another suitable component. At 102 the voltage of the towedvehicle battery is detected. At 104 the voltage is compared to a voltagethreshold V_(T). When the voltage is over the threshold, then it isinferred that the towed vehicle engine is running and that there is analternator or generator applying a higher voltage power to the battery.If so, then at 106 the brake drive system is turned off. The brake drivesystem, as described above, is connected to a brake pedal connector toactuate the brakes of the towed vehicle through the brake pedalconnector. As a result, when a user starts the vehicle, the brake drivesystem is turned off and the user will have complete control over thevehicle's brakes as the vehicle is being driven.

At 104 if the voltage is not over the threshold V_(T), then the brakedrive system is turned on at 108 or remains on if it is already on. Thisallows the towed vehicle braking system to operate the brakes while thevehicle is being towed.

In some embodiments, while the towed vehicle braking system is on andhas power from the towed vehicle battery, the internal inertial sensors341 detect accelerations in one or more axes at 110. If there is noacceleration in any axis after some predetermined time duration T_(D),then it may be inferred that the towed vehicle has been parked. At 112if there is no acceleration within T_(D) or before the expiration ofT_(D), then the brake drive system may also be turned off at 110. Thismay be a lower power sleep mode. The process then waits for anotherinstance of acceleration at 112, a manual turn-on signal, or anotherwake up command to turn on the brake drive system. When acceleration isdetected, then the process goes to 102 to determine the battery voltageand turn the brake drive system on or off as described above.

The process of FIG. 10 allows the towed vehicle braking system to beused without a user ever needing to turn the system on or off. It turnsoff when the vehicle is driven and it turns off when the vehicle isparked. It is on only when the vehicle is turned off but is experiencingaccelerations. These are the kind of accelerations that would beexperienced when the vehicle is being towed by another vehicle. Thisavoids a risk that a user will forget to turn the system on or off andit eliminates any inconvenience to the user of reaching for a switchsomewhere to turn the system on or off.

FIG. 11 is a process flow diagram for controlling the operation of thebrake drive system air pump and valve manifold. The process may beperformed by the main processor 344 or by a processor of the brake drivesystem 304 in response to inputs from inertial sensors 341, a breakawaydetector 308, and other components. At 122 inertial sensors determinewhether the towed vehicle is decelerating. If so, then at 128, the brakedrive system applies a positive pressure to the vehicle brake pedal toapply the brakes. In some embodiments, this is done by activating theair pump or compressor, energizing a cylinder valve to connect the pumpto the cylinder, and venting a power booster valve to block flow to andfrom the power booster. In some embodiments, the booster valve allowsair to be drawn into the air pump. In some embodiments, the cylindervalve is connected between the cylinder and a pressure tank to pass airfrom the tank to the cylinder. The air pump is only used to replenishthe air tank. Other configurations may alternatively be used. Afterbraking, the process returns to 122.

If the vehicle is not decelerating, then at 124, the process determinesif there is a vehicle breakaway. If so, suggesting that the towedvehicle is no longer attached to the tow vehicle but is moving along theroad with no driver or controls, then at 128, the brake drive system isactivated as described above. If there is no deceleration and no vehiclebreakaway, then at 126, the vacuum pressure of the brake power boosteris checked. If the vacuum pressure is low e.g. the pressure is less thana predetermined pressure threshold P_(VT), then the air pump isactivated to replenish the vacuum. The pump is activated, the boostervalve is vented to allow air to be drawn from the booster reservoir andthe cylinder valve is vented to allow air from the booster to be pumpedto ambient. After braking, the process then returns to 122.

If there is no deceleration at 122, no vehicle breakaway at 124, and nolow vacuum pressure at 126, then the process goes to an active statestanding by at 132. The pump is deactivated, the cylinder valve isvented and the booster valve is vented. The process returns to 122 forthe next deceleration and braking event. While this process is presentedas flow chart, it may also be implemented as different states or as aresponse to alerts with priorities. As an example, each of the tests at122, 124, 126 may be received at a decision instance as an alert. Thebreakaway alert might have the highest priority so that braking happensregardless of inertial events and the state of the power booster. Thedeceleration alert might have the next highest priority so that brakingoccurs regardless of the power booster state. The power booster vacuumalert has the lowest priority so that the vacuum booster is replenishedonly if there is no braking event.

A towed vehicle braking system is described that in some embodimentsincludes a brake pedal connector configured to connect to a brake pedalof a brake of a towed vehicle. A cylinder has a piston connected to thebrake pedal connector to actuate the brake of the towed vehicle throughthe brake pedal connector by applying a positive pressure to the brakepedal connector to move the brake pedal. A vacuum supply line is coupledto a power booster of the towed vehicle brake and configured to providevacuum to the power booster. A pump is coupled to the vacuum supply lineand to the cylinder to alternately provide vacuum to the vacuum supplyline and to drive the piston to actuate the brake. An inertial sensordetects deceleration of the towed vehicle, and a processor is coupled tothe inertial sensor and to the pump to cause the pump to not providevacuum and to drive the piston in response to the detection ofdeceleration.

In some embodiments the system includes a vacuum sensor coupled to theprocessor to measure vacuum at the power booster and wherein theprocessor causes the pump to provide vacuum if the measured vacuum isbelow a threshold. In some embodiments the processor causes the pump toprovide vacuum only if the measured vacuum is below a threshold and thepiston is not being driven in response to the detection of deceleration.

In some embodiments the system includes a vacuum valve between the pumpand the vacuum supply line and coupled to the processor to couple thepump to the vacuum supply line if deceleration is not detected, and acylinder valve between the pump and the cylinder and coupled to theprocessor to couple the pump to the cylinder if deceleration isdetected. In some embodiments the system includes a manifold attached tothe pump, wherein the manifold comprises the vacuum valve and thecylinder valve.

In some embodiments the cylinder is a pneumatic cylinder, wherein thevacuum valve is opened to atmosphere to provide air to the pump to applyair pressure to the cylinder and wherein the cylinder valve is opened toatmosphere to provide a vent to the pump to apply vacuum to the powerbooster. In some embodiments the system includes a vacuum pressuresensor coupled to the vacuum supply line to sense the vacuum pressure ofthe power booster and coupled to the processor. In some embodiments theprocessor is configured to operate in a first state if deceleration isnot detected and a second state if deceleration is detected, in thefirst state the processor causing the pump to maintain vacuum at thepower booster above a threshold, in the second state the processorcausing the pump to drive the piston and not generate vacuum.

Some embodiments pertain to a method that includes detectingdeceleration of a towed vehicle at an inertial sensor of a towed vehiclebraking system, detecting vacuum pressure at a power booster of thetowed vehicle, and determining whether the detected vacuum pressure isbelow a predetermined vacuum threshold. If the detected vacuum pressureis below the predetermined vacuum threshold and if deceleration is notdetected, then a pump coupled to the power booster is operated to supplyvacuum to the power booster.

In some embodiments the method includes if deceleration is detected thenoperating the pump to drive a brake actuation system coupled to the pumpto actuate a brake of the towed vehicle regardless of the booster vacuumpressure. In some embodiments operating the pump to supply vacuumcomprises operating the pump to supply vacuum only if the pump is notoperated to drive a brake actuation system. In some embodiments themethod includes if vehicle breakaway is detected then operating the pumpto drive a brake actuation system to actuate a brake of the towedvehicle regardless of the booster vacuum pressure. In some embodimentsthe method includes stopping operation of the pump if the vacuumpressure is above the predetermined vacuum pressure.

Some embodiments pertain to a towed vehicle braking system that includesa pneumatic brake actuator to actuate the brake of a towed vehiclethrough a brake pedal connector by applying a positive pressure to thebrake pedal connector to move the brake pedal, a vacuum supply linecoupled to a power booster of the towed vehicle brake and configured toprovide vacuum to the power booster, an air pump coupled to the vacuumsupply line and to the pneumatic brake actuator to alternately providevacuum to the vacuum supply line and to drive the piston to actuate thebrake, and a processor coupled to the air pump to control the operationof the vehicle braking system. The processor causes the braking systemto enter a brake state in which the air pump drives the pneumatic brakeactuator and does not provide vacuum to the vacuum supply line, and abooster state in which the air pump provides vacuum to the vacuum supplyline and does not drive the pneumatic brake actuator.

In some embodiments the processor further causes the braking system toenter an active state in which the air pump does not drive the pneumaticbrake actuator and does not provide vacuum to the vacuum supply line. Insome embodiments the system includes an inertial sensor to detectdeceleration of the towed vehicle and wherein the processor cause thebraking system to enter the brake state in response to deceleration. Insome embodiments the system includes a power booster vacuum sensor tosense the vacuum of the vacuum supply line and wherein the processorcauses the braking system to enter the booster state in response tosensed vacuum being below a predetermined vacuum threshold.

In some embodiments the processor causes the braking system to exit thebooster state and enter the brake state in response to deceleration ofthe towed vehicle. In some embodiments the deceleration of the towedvehicle is detected by an accelerometer coupled to the processor. Insome embodiments the system includes a vehicle breakaway detector andwherein the processor causes the braking system to enter a breakawaystate in response to a detected vehicle breakaway in which the air pumpdrives the pneumatic brake actuator and does not provide vacuum to thevacuum supply line.

While the present description is provided in the context of an installedbraking system, many of the structures, features and operations may alsobe used with a portable towed vehicle braking system. In embodiments, aportable towed vehicle braking system may be connected to a vehicleinterior power socket to obtain power to operate the braking system. Thevoltage at this interior power socket will be very similar to the powerat the battery. The portable braking system may have a wired or wirelessconnection to a breakaway cable and may be operated using a portablecontrol panel.

A lesser or more equipped brake activation system and wirelesscommunication systems than the examples described above may be desirablefor certain implementations. Therefore, the configuration of the systemwill vary from implementation to implementation depending upon numerousfactors, such as price constraints, performance requirements,technological improvements, and/or other circumstances.

While the steps described herein may be performed under the control of aprogrammed processor, such as central processing unit, a microcontrolleror by any programmable or hardcoded logic, such as Field ProgrammableGate Arrays (FPGAs), TTL logic, or Application Specific IntegratedCircuits (ASICs), for example. Additionally, the methods of the presentinvention may be performed by any combination of programmed generalpurpose computer components and/or custom hardware components.Therefore, nothing disclosed herein should be construed as limiting thepresent invention to a specific combination of hardware components.

The present description presents the examples using particular terms,such as towed vehicle, breakaway, breakaway detector, brake pedal,actuation arm, arm drive, sensor, switch, etc. These terms are used toprovide consistent, clear examples, however, the present invention isnot limited to any particular terminology. Similar ideas, principles,methods, apparatus, and systems can be developed using differentterminology in whole, or in part. In addition, the present invention canbe applied to ideas, principles, methods, apparatus, and systems thatare developed around different usage models and hardware configurations.

In the present description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, the present inventioncan be practiced without some of these specific details. In otherinstances, well-known structures and devices are shown in block diagramform. The specific detail can be supplied by one of average skill in theart as appropriate for any particular implementation.

The present invention includes various steps, which can be performed byhardware components or can be embodied in machine-executableinstructions, such as software or firmware instructions. Themachine-executable instructions can be used to cause a general-purposeor special-purpose processor programmed with the instructions to performthe steps. The machine-executable instructions may be stored in acontroller or in a separate memory. Alternatively, the steps can beperformed by a combination of hardware and software.

Aspects of the present invention can be provided as a computer programproduct that can include a machine-readable medium having instructionsstored thereon, which can be used to program a computer (or othermachine) to perform a process according to the present invention. Themachine-readable medium can include, but is not limited to, floppydiskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs,RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, or anyother type of medium suitable for storing electronic instructions.

Although this disclosure describes illustrative embodiments of theinvention in detail, it is to be understood that the invention is notlimited to the precise embodiments described. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense. Various adaptations, modifications and alterationsmay be practiced within the scope of the invention defined by theappended claims.

What is claimed is:
 1. A towed vehicle braking system comprising: abrake pedal connector configured to connect to a brake pedal of a brakeof a towed vehicle; a cylinder having a piston connected to the brakepedal connector to actuate the brake of the towed vehicle through thebrake pedal connector by applying a positive pressure to the brake pedalconnector to move the brake pedal; a vacuum supply line coupled to apower booster of the towed vehicle brake and configured to providevacuum to the power booster; a pump coupled to the vacuum supply lineand to the cylinder to alternately provide vacuum to the vacuum supplyline and to drive the piston to actuate the brake, but not both at thesame time; an inertial sensor to detect deceleration of the towedvehicle; and a processor coupled to the inertial sensor and to the pumpto cause the pump to not provide vacuum to the vacuum supply line and todrive the piston in response to the detection of deceleration.
 2. Thesystem of claim 1, further comprising a vacuum sensor coupled to theprocessor to measure vacuum at the power booster and wherein theprocessor causes the pump to provide vacuum if the measured vacuum isbelow a threshold.
 3. The system of claim 2, wherein the processorcauses the pump to provide vacuum only if the measured vacuum is below athreshold and the piston is not being driven in response to thedetection of deceleration.
 4. The system of claim 1, further comprising:a vacuum valve between the pump and the vacuum supply line and coupledto the processor to couple the pump to the vacuum supply line ifdeceleration is not detected; and a cylinder valve between the pump andthe cylinder and coupled to the processor to couple the pump to thecylinder if deceleration is detected.
 5. The system of claim 4, furthercomprising a manifold attached to the pump, wherein the manifoldcomprises the vacuum valve and the cylinder valve.
 6. The system ofclaim 4, wherein the cylinder is a pneumatic cylinder, wherein thevacuum valve is opened to atmosphere to provide air to the pump to applyair pressure to the cylinder and wherein the cylinder valve is opened toatmosphere to provide a vent to the pump to apply vacuum to the powerbooster.
 7. The system of claim 1, further comprising a vacuum pressuresensor coupled to the vacuum supply line to sense the vacuum pressure ofthe power booster and coupled to the processor.
 8. The system of claim1, wherein the processor is configured to operate in a first state ifdeceleration is not detected and a second state if deceleration isdetected, in the first state the processor causing the pump to maintainvacuum at the power booster above a threshold, in the second state theprocessor causing the pump to drive the piston and not generate vacuum.9. A method comprising: detecting deceleration of a towed vehicle at aninertial sensor of a towed vehicle braking system; detecting vacuumpressure at a power booster of the towed vehicle; determining whetherthe detected vacuum pressure is below a predetermined vacuum threshold;and if the detected vacuum pressure is below the predetermined vacuumthreshold and if deceleration is not detected, then operating a pumpcoupled to the power booster to supply vacuum to the power booster. 10.The method of claim 9, further comprising if deceleration is detectedthen operating the pump to drive a brake actuation system coupled to thepump to actuate a brake of the towed vehicle regardless of the boostervacuum pressure.
 11. The method of claim 9, wherein operating the pumpto supply vacuum comprises operating the pump to supply vacuum only ifthe pump is not operated to drive a brake actuation system.
 12. Themethod of claim 9, further comprising if vehicle breakaway is detectedthen operating the pump to drive a brake actuation system to actuate abrake of the towed vehicle regardless of the booster vacuum pressure.13. The method of claim 9, further comprising stopping operation of thepump if the vacuum pressure is above the predetermined vacuum pressure.14. A towed vehicle braking system comprising: a pneumatic brakeactuator to actuate the brake of a towed vehicle through a brake pedalconnector by applying a positive pressure to the brake pedal connectorto move the brake pedal; a vacuum supply line coupled to a power boosterof the towed vehicle brake and configured to provide vacuum to the powerbooster; an air pump coupled to the vacuum supply line and to thepneumatic brake actuator to alternately provide vacuum to the vacuumsupply line and to drive the piston to actuate the brake; and aprocessor coupled to the air pump to control the operation of thevehicle braking system, the processor causing the braking system toenter a brake state in which the air pump drives the pneumatic brakeactuator and does not provide vacuum to the vacuum supply line, and abooster state in which the air pump provides vacuum to the vacuum supplyline and does not drive the pneumatic brake actuator.
 15. The system ofclaim 14, wherein the processor further causes the braking system toenter an active state in which the air pump does not drive the pneumaticbrake actuator and does not provide vacuum to the vacuum supply line.16. The system of claim 14, further comprising an inertial sensor todetect deceleration of the towed vehicle and wherein the processor causethe braking system to enter the brake state in response to deceleration.17. The system of claim 14, further comprising a power booster vacuumsensor to sense the vacuum of the vacuum supply line and wherein theprocessor causes the braking system to enter the booster state inresponse to sensed vacuum being below a predetermined vacuum threshold.18. The system of claim 17, wherein the processor causes the brakingsystem to exit the booster state and enter the brake state in responseto deceleration of the towed vehicle.
 19. The system of claim 18,wherein the deceleration of the towed vehicle is detected by anaccelerometer coupled to the processor.
 20. The system of claim 14,further comprising a vehicle breakaway detector and wherein theprocessor causes the braking system to enter a breakaway state inresponse to a detected vehicle breakaway in which the air pump drivesthe pneumatic brake actuator and does not provide vacuum to the vacuumsupply line.